This invention relates to a method and apparatus for measuring the calorific value of a gas.
The gas may be a fuel gas, for example natural gas. The natural gas may be methane and may further comprise nitrogen and/or carbon dioxide. In addition to methane the natural gas may comprise at least one other hydrocarbon gas, for example ethane, propane, butane, pentane or hexane.
According to one aspect of the invention, a method of measuring the calorific value of a gas comprises making a measure of the speed of sound in the gas and using the speed of sound in an operation producing the calorific value corresponding to said speed of sound.
According to another aspect of the invention a method of measuring the calorific value of a gas comprises making a measure of the speed of sound in the gas, making a measure of a first thermal conductivity of the gas at a first temperature, making a measure of a second thermal conductivity of the gas at a second temperature which differs from the first temperature, and using the speed of sound and the first and second thermal conductivities in an operation producing the calorific value of the gas corresponding to said speed of sound and said first and second thermal conductivities.
According to a further aspect of the invention an apparatus to measure the calorific value of a gas comprises means to measure the speed of sound in the gas and means to use the speed of sound in an operation producing the calorific value of the gas corresponding to said speed of sound.
According to a still further aspect of the invention an apparatus to measure the calorific value of a gas comprises means to measure a first thermal conductivity of the gas at a first temperature; means to measure a second thermal conductivity of the gas at a second temperature which differs from the first temperature, and means using the speed of sound and the first and second thermal conductivities in an operation producing the calorific value of the gas corresponding to said speed of sound and said first and second thermal conductivities.